Sensors are used to view objects and/or ambient conditions in varied environments and often under severe conditions. Millimeter wave, visible and infra-red sensors are used to guide supersonic missiles through the atmosphere to intercept reentry vehicles. Radiometers are required to assess radiation heat transfer of aerobrake vehicles as the vehicle re-enters the atmosphere. In high temperature manufacturing processes, plasma furnaces, rocket engines and the like heat flux, radiation characteristics, and temperature are required to be observed and measured. Sensor's are also used to observe nuclear explosions and become exposed to gamma rays and particles, high intensity light and infra-red radiation.
Severe environments place constraints on sensor design and the apertures through which the sensor's view or measure conditions. To protect the sensors from damage, special techniques have been used: Cooled, high temperature windows, protective shrouds and special cooling techniques have been used, all of which incur increased cost, add weight, and detract from the sensor's performance. Further, time dependent temperature changes and gradients in the sensor's protective observation window changes the window's refractive index, causing image distortion and dispersion.
Current requirements for protecting sensors in interceptor vehicle application, while permitting a wide field of regard, on the order of tens of degrees or so, and modest fields of view, on the order of degrees necessitates complex arrangements of high temperature high strength transparent windows formed of costly specialized materials, special relay mirrors located between the window and sensor, and/or special cooling techniques to protect the windows and sensor from exceptionally high aerodynamic heat flux and pressure. In particular, the coolant and coolant flow control systems represent a substantial fraction of the weight of the interceptor; and the volume required to house the cooling and flow control system adds substantially to the mass, size and cost of the interceptor. Coolant flow over the observation window induces turbulence and refractive effects that degrade the image.
One technique devised to provide protection for the sensor is to modify the nose cones structure to form a deep depression or well in the fore section of the nose cone. The sensor is placed at the bottom of that well. As a consequence the heating of the sensor that occurs from the friction of onrushing air is reduced. That technique requires the sensor to be placed along the longitudinal axis of the nose cone. It is less effective and may be ineffective when used in a non-symmetric orientation and at non-zero angles of attack. Because the sensor is deeply embedded in the nose cone, the sensor's field of view is necessarily limited and the space vehicles overall length and, hence, mass is necessarily larger than otherwise. Because the nose cone geometry is modified for the foregoing technique, concerns develop as to the effects on aerodynamic control, thermal control and protection of the nose cone tip region and must be addressed.
Another technique proposed is to employ a "jettisonable" shroud to protect the sensor during atmospheric flight. When the space vehicle attains a sufficiently high altitude, the shroud is jettisoned, typically with an explosive device, uncovering the sensor. The sensor is then used at near-vacuum condition, where heat and pressure are insignificant. At best, this technique is believed to be impractical. For endoatmospheric interception, the technique is ineffective.
An object of the invention is to protect a radiant energy sensor from damage as could be caused by sensing applications in harsh environments.
Another object of the invention is to provide the sensor apparatus for use in missiles capable of providing images whose quality is not degraded by thermal effects or require levels of coolant characteristic of the prior sensors in that application.
An additional object of the invention is to provide a support structure of simple construction for mounting a sensor that permits the sensor to be displaced or offset from the environment being sensed so as to at least partially isolate the sensor from such environment and, thereby protect the sensor from physical damage, without adversly affecting the integrity of readings supplied by the sensor.
As further background, U.S. Pat. No. 3,657,284 granted Mar. 7, 1972 to Elings and Landry discloses an optical display device in which a small colored marble reposed in a cavity appears as a real image of the marble located in a position above the device, giving the illusion that the marble is positioned where it is not and allowing one to run one's hand through a seemingly solid object to one's amusement. To accomplish that illusion the cavity walls are defined by two parabaloid mirrored surfaces, the upper or top surface at which the image appears containing a central aperture, and the focus of the upper paraboloid being coincident in position with the vertex of the bottom wall, on which the marble is positioned. The foregoing novelty device showed a structure as would produce a real image of an object confined in the cavity to the outside to astonish and serve to amuse the lay person.
The present invention builds upon the principles inherent in the foregoing discovery in a novelty device that is unrelated to sensor apparatus, and provides a unique sensor support structure that offsets the position of the sensor and thereby protects the sensor from physical damage or degradation from the environment being sensed, and thereby provide a new and useful sensor apparatus.